Fix chained access to multi-dimensional hash

lib/liquid/parser.rb

@@ -75,7 +75,7 @@ module Liquid
 
     def variable_signature
       str = consume(:id)
-      if look(:open_square)
+      while look(:open_square)
         str << consume
         str << expression
         str << consume(:close_square)

test/integration/output_test.rb

@@ -44,6 +44,14 @@ class OutputTest < Minitest::Test
     assert_equal expected, Template.parse(text).render!(@assigns)
   end
 
+  def test_variable_traversing_with_two_brackets
+    text = %({{ site.data.menu[include.menu][include.locale] }})
+    assert_equal "it works!", Template.parse(text).render!(
+      "site" => { "data" => { "menu" => { "foo" => { "bar" => "it works!" } } } },
+      "include" => { "menu" => "foo", "locale" => "bar" }
+    )
+  end
+
   def test_variable_traversing
     text = %| {{car.bmw}} {{car.gm}} {{car.bmw}} |